THMX Document — A .thmx file is a THMX Document. It is a document format used for word processing, spreadsheets, presentations or ebooks.
Quick facts
What is .thmx
A .thmx file is a THMX Document. It is a document format used for word processing, spreadsheets, presentations or ebooks.
In the mime-db registry it maps to application/vnd.ms-officetheme. When serving .thmx over HTTP, set the Content-Type header as shown in Developer info below.
Related entities: it maps to application/vnd.ms-officetheme — and is delivered over HTTP via the Content-Type header.
How to open .thmx files
Developer info
When served over HTTP, responses should set the following header:
Content-Type: application/vnd.ms-officetheme
Common software that reads/writes .thmx:
Relation chain
Related extensions
Related MIME types
Common uses
How to edit .thmx files
How to create .thmx files
Frequently asked questions
Common options include Microsoft 365, LibreOffice, Adobe Acrobat. You can also open many of these files with built-in viewers or a browser.
Create a new file in any text editor or the app that owns the format and save it with the .thmx extension.
application/vnd.ms-officetheme is the media type identifier used for .thmx files during network transfer (for example in the HTTP Content-Type header).
Sources & standards
Updated 2026-08-18
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